Summary

The HTML summary element (<summary>) is used as a summary, caption, or legend for the content of a <details> element.

Note: If the <summary> element is omitted, the heading "details" will be used.

Note: The default style for <summary> is display:list-item per HTML standard. If the style is being changed to display:block, the disclosure triangle will be dismissed, which is expected. See Bug 1283989 for more information.

[1] This feature is available since Firefox 47 behind the preference dom.details_element.enabled, defaulting to false, except on Nightly and Aurora versions (bug 1241750). Support for it is enabled by default, i.e. the preference is defaulting to true, since Firefox 49.0 (bug 1226455).